Mailspring/internal_packages/ui-dark/styles/ui-variables.less

@gray-base:    #ffffff;
@gray-darker:  darken(@gray-base, 13.5%); // #222
@gray-dark:    darken(@gray-base, 20%);   // #333
@gray:         darken(@gray-base, 33.5%); // #555
@gray-light:   darken(@gray-base, 46.7%); // #777
@gray-lighter: darken(@gray-base, 92.5%); // #eee
@white:        #0a0b0c;

@background-off-primary: #333;
@background-secondary:   #2D2D2D;
@background-tertiary:    #6d7987;

@background-primary:     #313131;
@background-color:       darken(#313131, 15%);
@btn-default-bg-color:   #404040;
@accent-primary:         #5AA8FA;
@accent-primary-dark:    #3087E1;

@text-color:                      #C2C2C2;
@text-color-subtle:               fadeout(@text-color, 20%);
@text-color-very-subtle:          fadeout(@text-color, 40%);
@text-color-inverse:              white;
@text-color-inverse-subtle:       fadeout(@text-color-inverse, 20%);
@text-color-inverse-very-subtle:  fadeout(@text-color-inverse, 50%);
@text-color-heading:              #FFF; 

@border-primary-bg:     lighten(@background-primary, 10%);
@border-secondary-bg:   lighten(@background-secondary, 10%);
@border-tertiary-bg:    lighten(@background-tertiary, 10%);
@border-color-divider:  @border-secondary-bg;

@input-bg:              #242424;
@input-border:          @border-color-divider;

@list-bg:               #333;
@list-border:           #383838;

@list-selected-color:   @text-color-inverse;

@toolbar-background-color: @background-secondary;

.thread-icon:not(.thread-icon-unread) {
  -webkit-filter: invert(100%);
}
img.content-dark {
  -webkit-filter: invert(100%);
}
img.content-light {
  -webkit-filter: invert(100%);
}